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The Seventh Cranial Nerve
The Facial
By
Prof. Dr. Muhammad Imran Qureshi
Functional Components:
SVE: Fibers originate from nucleus of facial
nerve, and supply facial muscles
GVE: Fibers derived from superior
salivatory nucleus and relayed in
pterygopalatine and submandibular ganglia.
The postganglionic fibers supply lacrimal,
submandibular and sublingual glands.
refers to its position between the motor root
and cranial nerve VIII.
The special visceral motor root and nervus
intermedius enter the internal acoustic
meatus in the petrous temporal bone along
with the VIII cranial nerve.
All three are enveloped by an arachnoid /
dural sheath that extends the length of the
SVA: Fibers from taste buds of anterior two
thirds of tongue with cell bodies in the
geniculate ganglion of the facial nerve end
by synapsing with cells of nucleus of
solitary tract
GSA: Fibers from skin of external ear.
The facial nerve arises by two roots from the
brainstem (Pons) in the posterior cranial
fossa.
Figure 2: Facial Nerve in the Petrous Part of Temporal Bone
meatus.
The nervus intermedius and motor root of
the facial join to form the complete facial
nerve just before the end of the meatus, and
this complete nerve pierces the arachnoid
and dura to enter the facial canal.
The facial canal runs anterolaterally in the
petrous bone for one or two millimeters and
then comes upon the labyrinthine wall of the
tympanic cavity.
Here the facial nerve bifurcates in two forks
that move off in opposite directions
perpendicular to the path of their parent
nerve.
Figure 1: Nuclei of the Facial Nerve in Pons
Like the trigeminal nerve, one root is special
visceral motor. But unlike the trigeminal
nerve, the other contains preganglionic
parasympathetic axons as well as sensory
axons. The other name of this root is the
“nervus intermedius”. It gives no
information about fiber type. Rather, it
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The larger fork passes posterolaterally and
the smaller passes anteromedially.
Both forks run parallel to the long axis of
petrous temporal bone.
At the site of the bifurcation there is a
collection of cells that form the sensory
ganglion of the facial nerve.
The larger fork retains the name “facial
nerve” and the channel within the petrous
bone through which it travels retains the
name “facial canal”.
When the facial nerve encounters the
labyrinthine wall of the tympanic cavity it
undergoes a 90o bend in its course that takes
it posterolaterally.
Upon reaching the bony mastoid wall of the
tympanic cavity, the facial nerve passes
below the aditus ad antrum into this wall.
The nerve then continues downward in the
mastoid wall of the tympanic cavity to
emerge from the stylomastoid foramen.
Near the vicinity of the geniculate ganglion,
the facial nerve gives off a tiny twig that
participates in a nerve plexus that lies
beneath the mucous membrane that covers
the promontory of the tympanic cavity.
The plexus is called the tympanic plexus,
and it receives its main input from the
tympanic branch of the glossopharyngeal
nerve. The internal carotid plexus also sends
a caroticotympanic nerve backwards to join
in the tympanic plexus.
Figure 2: Intracranial Course of the Facial Nerve
This bend is called the genu of the facial
nerve (Lt: knee).
That is why the sensory ganglion located at
the facial bifurcation is most often called the
“geniculate ganglion”.
Beyond the geniculate ganglion the facial
nerve runs posterolaterally in the bone that
forms the labyrinthine wall of the tympanic
cavity.
This course takes it above the oval window
but inferior to the lateral semicircular canal
to the mastoid wall of the tympanic cavity.
While it descends in the mastoid wall of the
middle ear cavity, the facial nerve gives off
two branches.
The first one is the minute nerve to the
stapedius muscle.
The second one “the chorda tympani” is
given off a little further along its descent.
This nerve passes forward out of the bony
mastoid wall into the tympanic cavity (but
remains outside its mucous membrane).
Here it continues anteriorly, crossing lateral
to the long process of the incus and then
medial to the neck of the malleus.
Figure 3: Intracranial branches of the Facial Nerve
Figure 4: The Chorda Tympani
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The chorda tympani then passes out of the
carotid wall of the tympanic cavity through
a slit (petrotympanic fissure) that leads to
the infratemporal fossa just behind the
medial end of the jaw joint.
Upon exiting the skull through the
stylomastoid foramen, the facial nerve enters
the retromandibular region of the neck.
Its course beyond this point is linked to the
lingual branch of VIII.
The chorda tympani carries:


Preganglionic parasympathetic axons
for the submandibular and sublingual
salivary glands, and
Taste fibers from the anterior two
thirds of the tongue.
While traveling in the mastoid wall of the
tympanic cavity, the facial nerve also sends
a small twig to communicate with the
Figure 6: Ansa Facialis
Here it gives branches to the auricularis
posterior, stylohyoid, and the posterior belly
of digastric muscles.
After these are given off, the nerve enters
the parotid gland and divides into upper and
lower divisions, which turn forward, pass
lateral to the retromandibular vein, and
thereby reach the part of the parotid lying in
the face.
Here, within the gland, the two divisions
join again to form the “ansa facialis.”
Figure 5: Extracranial Course & Branches of the
Facial Nerve
auricular branch of the vagus.
This twig carries somatic sensory axons
from the external auditory meatus.
From this loop spray out the branches of the
facial nerve to the remaining facial muscles.
These branches are given names according
to the general area of the face to which they
run (temporal, zygomatic, buccal,
mandibular, cervical).
The smaller, anteromedially coursing fork of
the facial nerve is called the greater
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superficial petrosal nerve.
As soon as the nerve of the pterygoid canal
enters this fossa, it encounters the
pterygopalatine ganglion, on whose cells the
preganglionic parasympathetic axons
synapse.
The postganglionic parasympathetic axons
from the ganglion are distributed with
branches of the maxillary nerve.
Some of these enter the zygomatic nerve and
are carried into the orbit, where they cross to
the lacrimal branch of VI for supply of the
lacrimal gland.
Figure 7: Course & Distribution of the Facial Nerve
It emerges into the middle cranial fossa on
the anterior surface of the petrous temporal
(between bone and endocranium) through a
hole called the hiatus of the facial canal.
From here, its course continues across the
depth of the trigeminal ganglion and onto
the cartilage that fills the foramen lacerum,
where the nerve is located just lateral to the
internal carotid artery.
Here, postganglionic sympathetic fibers
from the internal carotid plexus join the
greater superficial petrosal nerve. These
sympathetic axons are said to form the deep
petrosal nerve.
The product of this joining will leave the
cranial cavity by passing obliquely through
the cartilage of the foramen lacerum to enter
a canal in the sphenoid bone at the root of
the medial pterygoid plate.
This is the pterygoid canal, and the bundle
formed by the conjoined deep petrosal and
greater superficial petrosal nerves is called
the nerve of the pterygoid canal.
The pterygoid canal ends by opening into
the pterygopalatine fossa located
inferomedial to the foramen rotundum.
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The postganglionic sympathetic axons
within the nerve of the pterygoid canal pass
right through the pterygopalatine ganglion,
without synapse, to distribute with branches
of the maxillary nerve.
The taste fibers from the palate travel
through palatine nerves up to the ganglion,
and then pass through it into the nerve of
pterygoid canal and greater superficial
petrosal nerve, which carries them to their
cells of origin in the geniculate ganglion.
CLINICAL CONSIDERATIONS:
The symptoms of damage to the facial nerve
depend on where along its course the
damage has occurred.
One of the most common sites is the region
of the facial canal just above the
stylomastoid foramen.
Here, an inflammatory disease of unknown
etiology causes a condition known as Bell's
palsy.
All the facial muscles on one side are
paralyzed, but the glandular and taste
functions of the facial nerve remain intact.
Bell’s palsy is characterized by a multitude
of symptoms that can be predicted from
paralysis of facial muscles:
In older persons, in whom elasticity of skin
is diminished, paralysis of facial muscles
causes the normal creases in facial skin to be
diminished or absent on the affected side.
In all persons, both young and old, the eye
of the affected side cannot be completely
closed.
Because blinking is impossible, the normal
cleansing of the surface of the eye is
impossible.
The lacrimal gland increases its secretion in
an attempt to compensate.
However, without blinking, the tears are not
distributed toward the lacrimal puncta.
Furthermore, paralysis of the lacrimal
portion of orbicularis oculi causes the
lacrimal puncta to lift off the surface of the
eyeball, and paralysis (or loss of passive
elasticity) of the palpebral orbicularis oculi
of the lower lid causes it to fall forward
away from the eye.
The effect of all these changes is for the
excess tears to pool beneath the lower lid
and then spillover onto the cheek.
The corner of the mouth and the lower lip
droop on the side of the paralysis, allowing
saliva to run out of the mouth.
Paralysis of the buccinator allows food to
accumulate between the cheek and lower
gum.
The patient prefers to chew on the un
paralyzed side, but often must manually
push on the lower cheek of the affected side
in order to express food out of the oral
vestibule.
Occasionally, a facial paralysis may be
psychosomatic in nature. It can be diagnosed
by availing oneself of the oculoauricular
reflex. Normally, when a person looks very
strongly to one side, the opposite ear is
pulled back by the auricularis posterior
muscle. This reflex is absent in Bell's palsy,
but it is intact if the facial paralysis is
psychosomatic.
Pathology of the facial nerve within the
facial canal may extend upward to involve
the communicating twig to the vagus and the
origin of the chorda tympani.
Since so many other nerves provide
sensation to the external auditory meatus,
loss of function in the “facial axons” that do
so is undetectable.
However, irritative lesions of, the facial
nerve may lead to pain in the external
auditory meatus. If the chorda tympani is
damaged, taste from the anterior two thirds
of the tongue will be lost (or greatly
diminished).
Figure 8: Facial Nerve Palsy (Bell’s Palsy)
The potential for irritation to the cornea is
great, and persons with a Bell's palsy must
wear an eye patch to keep the lids closed.
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Some patients with damage to the chorda
tympani also complain of partial numbness
of the tongue on the ipsilateral side. Progress
of the disease even more superiorly in the
facial canal leads to paralysis of the
stapedius and a resultant increased
sensitivity to loud sounds, known as
hyperacusis.
Tumors within the petrous temporal may
affect the facial nerve at the site of the
geniculate ganglion.
This leads to all the symptoms just
described, plus loss of tearing on the
affected side.
Lesions of the facial nerve between the brain
and the facial canal may affect one root and
not the other because the two roots are
actually separate during this part of their
courses.
There is a peculiarity about the cortical input
to the facial nuclei of the brainstem that is
useful in diagnostics.
The facial motor neurons projecting to the
upper third of the face receive cortical
control from both the right and left cerebral
hemispheres, whereas the facial motor
neurons to the lower two thirds of the face
receive cortical control only from the
opposite cerebral hemisphere.
Thus, if a facial paralysis is due to
interruption in the corticobulbar pathway on
one side, the symptoms due to paralysis of
the mouth and cheek on the opposite side are
full-blown, but the orbicularis oculi and
frontalis of this same side are not nearly as
weakened as in Bell’s palsy.
Testing of the facial nerve during a routine
physical examination is confined to
assessing the major facial muscles.
The patient is asked to raise the eyebrows or
wrinkle the forehead (occipitofrontalis) and
the examiner looks to see if this is done
symmetrically.
The patient is asked to close the eyes very
tightly (orbicularis oculi --- orbital and
palpebral portions) and the examiner tries to
force them open by pushing up on the
eyebrows.
A broad smile is requested (mainly
zygomaticus major) and assessed for
symmetry.
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The, patient is asked to puff out the cheeks.
Puffing out one's cheeks is made possible by
the action of orbicularis auris in preventing
escape of air between the lips. If one side is
very weak, air escapes on that side.
If air does not escape, the examiner applies a
test of strength by pushing in on both cheeks
to see if the orbicularis auris on one side can
be overwhelmed.
Only if these tests of facial muscles reveal
deficit does the examination progress to a
test of taste or lacrimation.
Taste on the anterior two thirds of the
tongue can be evaluated by applying a
strong tasting solution (e.g., salt, sugar,
citric acid, quinine) to its right and left
edges, where most of the taste buds are
concentrated.
There exist special absorbent paper strips
that can be applied to the surface of the eye
for assessing tear production.